This invention relates to transformers which are particularly suitable for use in pulse circuits in which a high current pulse at relatively low voltage is converted into a very high voltage pulse. A transformer of this kind can be used in a pulse circuit to provide the operating power for a high power oscillator, such as a magnetron, which forms part of a radar transmitter. Such a pulse circuit is sometimes termed a radar pulse modulator. A radar transmitter can transmit pulses having a very low mark-to-space ratio; that is to say, transmitted short pulses are spaced apart in time by relatively long intervals during which echoes of the pulses are retuned by intercepted targets to a radar receiver. The useful range of a radar is related to the power transmitted during the short pulse periods and it is therefore very important to maximize the power of these pulses, whilst ensuring that the pulses turn on and turn off cleanly without the generation of excessive noise. Following the turn off, or decay, of a transmitted short pulse, the receiver of the radar is enabled so that it can detect weak radar echoes. It is clearly important to ensure that the trailing edges of the transmitted short pulses decay very rapidly and cleanly so that they do not mask echoes received after only a very short delay from targets at very close range.
These requirements impose stringent demands on the pulse transformer itself as it may be required to convert an input pulse of only a few hundred volts to an output pulse voltage of up to 30 kV or even higher, whilst handling a peak pulse power of the order of two megawatts. It has been found that pulse transformers designed to meet these operating requirements may not be entirely satisfactory and can deteriorate unexpectedly quickly during operational use. The present invention seeks to provide an improved transformer which is suitable for use in a pulse circuit.